For a microwave transmission system, link availability is an important indicator for measuring link quality, where the availability refers to a percentage of remaining available time except unavailable time (in situations, such as a severe bit error and interruption of a link, which are caused because of channel deterioration, an equipment fault, human intervention, or other reasons) in total operating time of equipment. In an actual application, the link availability is affected by factors such as a weather change, or interference from an external signal. The availability is generally required to be greater than 99.99% in the microwave system.
In a current microwave transmission system, an adaptive modulation (Adaptive Modulation, AM) mode or an adaptive channel bandwidth (Adaptive Channel bandwidth, ACB) adjustment technology is a relatively frequently used method for improving link availability. When signal quality of a microwave link deteriorates, transmission capacity is reduced by reducing a sending modulation mode order, for example, 32 quadrature amplitude modulation (Quadrature Amplitude Modulation, QAM) is switched to 16QAM, or a channel bandwidth such as 250 M is switched to 125 M, so as to improve interference immunity of the system, and ensure stable service transmission, thereby improving the link availability. When the signal quality of the microwave link is desirable, the transmission capacity is improved by increasing a sending modulation mode order, for example, 16QAM is switched to 32QAM, or a channel bandwidth such as 125 M is switched to 250 M; however, interruption of the link may also be caused because decoding cannot be performed, and in this case, the link availability is affected.
As shown in FIG. 1, network equipment (Network Equipment, NE) includes a Tx Path module, an ACB Engine module, an Rx Path module, where the Tx Path/Rx Path module is configured to receive and send data, and calculate a mean square error (Mean Square Error, MSE) that identifies channel quality of a space link from a network element NE2 to a network element NE1, and the ACB Engine module is configured to monitor MSE information, and control the Tx Path/Rx Path module to perform bandwidth switching.
The network element NE1 is connected to the network element NE2, a link from NE2 to NE1 is Link A, and a link from NE1 to NE2 is Link B, where the Link A currently operates in a bandwidth of 250 M. The ACB Engine module of the network element NE1 monitors an MSE that reflects channel quality of the Link A and that is calculated by the Rx Path module, and obtains, according to the MSE and an MSE threshold for switching a target bandwidth, that the Link A may operate in a bandwidth of 500 M. The ACM Engine module sends, from the Link B through a channel provided by the Tx Path module, information that carries the target bandwidth, that is, a message about an adaptive channel bandwidth (Adaptive Channel bandwidth, ACB) of 500 M to the network element NE2. The ACM Engine module of the network element NE2 receives the information, which is sent by the network element NE1, about the target bandwidth of the Link A, and controls the Tx Path module of the NE2 and the Rx Path module of the NE1 to jointly complete switching of the Link A to the target bandwidth.
An operating bandwidth of the network element NE1 is 250 M. It is assumed that an interfering signal exists in a frequency domain range from a frequency band of 250 M to a frequency band of 500 M, and the interfering signal is already filtered out by a system anti-aliasing filter before being calculated by the ACB Engine, the network element NE2 sends a signal to the network element NE1 by using the Link A, and the interfering signal in the signal is filtered out by the system anti-aliasing filter; therefore, when the bandwidth is switched to 500 M, a bandwidth of the system anti-aliasing filter is also accordingly extended, and in this case, the interfering signal is in a passband of the system anti-aliasing filter and cannot be restricted by a system, thereby resulting in link interruption due to excessively large interference, and repeated ACB switching affects normal service transmission and link availability.